1. Field of the Invention
The present invention relates to an improvement in a process for producing a pulse generator which includes a stay of a substantially L-shaped section having a support plate portion secured to a stationary support and a mounting plate portion connected to the support plate portion, a cylindrical coil assembly including a coil wound around a bobbin, a core extending parallel to the support plate portion and surrounded by the coil assembly, a magnet clamped between a base end of the core and the mounting plate portion wherein, the stay, cylindrical coil assembly, core and magnet are coupled together by a synthetic resin in such a manner that a portion of the support plate portion projects, and that the tip end of the core is exposed to the outside.
2. Description of the Prior Art
Such pulse generators have been conventionally known, for example, from Japanese Utility Model Publication No.16304/88 and Japanese Patent Publication No.27908/90.
The stay of the pulse generator is mounted to the stationary support, so as to provide a given gap between the tip end of the core and a rotatable pulse rotor opposed to the tip end of the core. In order to maintain such gap constant, it is necessary to maintain at a constant distance the space between the fastened portion of the stay to the stationary support and the tip end of the core. However, it is difficult to maintain such a constant gap, because there are tolerances in size for the stay, the coil assembly and the magnet.
Thereupon, in the prior art pulse generator disclosed in Japanese Utility Model Publication No.16304/88, the synthetic resin is filled between the mounting plate portion of the stay and the magnet, and the tip end of the core is brought into abutment against the reference face of the mold with pushing the tip end by the synthetic resin filled between the mounting plate portion of the stay and the magnet during molding in the resin mold. In the prior art pulse generator disclosed in Japanese Patent Publication No.27908/90, the tip end of the core is brought into abutment against the reference face of the mold by pushing the magnet with a pin provided in the resin mold. With this process, the distance between the mounting plate portion of the stay and the tip end of the core can always be maintained constant. However, there is also a tolerance in size of the stay and hence, the distance between a mounting hole provided in the support plate portion of the stay and the tip end of the core is not necessarily constant. Therefore, when the stay has been mounted to the stationary support, a variation is produced in the gap between the tip end of the core and the pulse rotor. Moreover, in the prior art pulse generators disclosed in both the publications, an embedding process using the synthetic resin is carried out while keeping the core surrounded by the coil assembly and therefore, only the tip end of the core is received by the reference face of the resin mold. As a result, the force for retaining the core within the resin mold is weak; the core may be inclined by the pressure of the synthetic resin filled into the resin mold; and the breakage of the coil may occur.